This invention concerns a method that can be used to obtain great accuracy in writing text and pictures on a photosensitive surface with a light beam.
A light beam is used for writing in phototypesetting, preparation of printing plates, digital computer output, facsimile transmission, and in other tasks where one records pictorial or text material on a two-dimensional surface. When highly accurate output is required, a laser beam is employed, which results in high light intensity in a small spot. In this field, methods are previously known for the deflection and modulation of a laser beam in order to use it for writing. In these techniques, the control of the position of the beam is based on accurate mechanical motions and, in some solutions, on the signal given by a reference beam while it travels on a ruling. The required high accuracy, about 10,000-100,000 resolution elements in both dimensions on the image surface, cannot very easily be obtained in this manner.